Sequential hologram interferometry with diffusely illuminated objects

Two simple holographic multiplexing techniques for sequential hologram interferometry of a diffusely illuminated object are described. These techniques enable one to use the frozen-fringe hologram interferometry to study a quasi-continuous change in the object and so regain some of the advantages of real-time hologram interferometry. In the first method of multiplexing with a single reference beam, a small angle prism is used for varying the direction of the reference beam between successive exposures and a double-exposure hologram is recorded at each position of the prism. In the second method of multiplexing with multiple reference beams, a separate reference beam is used for recording each state of the object independently and the interference pattern between any two states is obtained by simultaneous reconstruction of two light fields. The advantage of this method over the previous one is that it is also suitable for dynamic studies. Some reconstructed interferograms of a diffusely illuminated transparent object under different stresses are presented as illustrations.     

基于双AOTF的新型成像光谱偏振探测系统

声光可调谐滤波器(AOTF)具有体积小、波长稳定性好、扫描范围宽、调制速度快等优点,在光谱成像中被广泛应用,但单独采用AOTF的成像光谱偏振探测还较少。为此提出只采用两个AOTF的成像光谱偏振探测新方法。该方法首先通过分束镜将入射光分成两束,两束光分别通过两个AOTF,而两个AOTF的正一级衍射光的偏振方向互成45°,由于AOTF的正一级衍射光的偏振方向互相垂直,因此两个AOTF的正负一级分别可得到0°,45°,90°和135°的光强,在测量中需保持两个AOTF的滤光所对应的波长完全相等。最后通过对两个AOTF的正负一级衍射成像,最终得到Stokes偏振信息中S₀(0°和90°光强和)、S₁(0°和90°光强差)和S₂(45°和135°光强差),结合相应的理论公式对被测目标的线偏振度(DoLP)和线偏振角(AoLP)实现成像。再通过对AOTF的射频驱动进行扫频,实现对被测目标不同波长偏振成像,最终实现成像光谱偏振探测。并通过对500,550和600 nm偏振成像进行实验验证。该方法具有无运动部件、无需转动、一次测量同时获得成像光谱偏振信息的优点。     

Influence of light polarization on the diffraction efficiency of TIR holograms

Normally when forming a TIR hologram two interference gratings are stored in the recording medium. The object beam interferes with the incoming and with the reflected reference beam. An appropriate selection of the polarization orientations of the interfering light beams leads to the suppression of one of the grating systems. Even to reconstruct TIR hologram it is not all the same in which orientation the reconstructing laser beam is polarized. With the proper selection of the polarization orientations of the forming and reconstructing laser light the diffraction efficiency for TIR holograms can be optimized.     

Spontaneous periodic structures induced in thin AgCl-Ag films by the continuum in the case of optical rotation of the plane of polarization

The formation of spontaneous periodic structures in thin AgCl-Ag films subject to the continuum (λ≈450–700 nm) in the case of rotation of the plane of polarization with the help of crystalline quartz is studied. The periodic structures are formed due to the excitation of waveguide TE₀ modes in spontaneous Rayleigh scattering of radiation with a wavelength λ incident on the film. The structure periods are smaller than λ and vary in proportion with λ. After special treatment of the irradiated sample (fixing and deposition of an Al layer), periodic structures form a thin reflection hologram capable of reproducing the direction of linear polarization, the angle of optical rotation, and the color of the spectrum recorded. The study of diffraction patterns and small-angle scattering from small portions of a hologram, which were exposed to light with various wavelengths in the recording process, with the help of a probing UV beam (λ_p=337 nm), made it possible to reveal special features of the manifestation of Rayleigh and Wood anomalies associated with the domain structure of PS.     

大功率高光斑均匀性半导体激光复合光源

 为了获得具有更高输出功率和良好光斑分布均匀性的半导体激光光源,根据半导体激光优良的偏振特性,利用偏振分光棱镜将2束大功率激光束合成为一束更大功率的光束,通过一个发射系统投射。在光束合成前采用非球面光学系统对每个激光器慢轴方向的光束进行扩束,使其与快轴方向光束发散角基本一致。实验证明,此种半导体激光复合光源具有良好的光斑均匀性,其输出功率是2个半导体激光器输出功率之和,完全满足激光制导等军用系统对激光功率和光斑均匀性的要求。     

Field asymmetry of the dynamic gain coefficient in organic photorefractive devices

The performance of amorphous organic photorefractive materials in holographic two-beam coupling experiments in the typical tilted geometry was found to be asymmetric with respect to the applied electric field direction. For one field direction, light is coupled into the polymer layer and can be detected on the side of the devices. For the other, the originally Gaussian-shaped writing beams show a shoulder or even split into two. The strength of the asymmetry depends on the diameter of the beams writing the hologram. We demonstrate that this effect is due to beam fanning. As a result of the fanning, the apparent photorefractive gain coefficients take on unphysical values.     

The effect of nonlinearity of the recording media response on the properties of thick phase holograms

The effect of nonlinearity of a photosensitive medium response on the diffraction properties of thick phase holograms is analyzed on the basis of coupled-wave equations. It is shown that, for a typical dependence of the refractive index on the exposure, the response nonlinearity lowers the diffraction efficiency of a hologram illuminated by an s-polarized light. For the p polarization of the reading beam, the response nonlinearity reduces the hologram efficiency when the angle between the beams diffracted into the zero and second orders (into the minus first and first orders) is smaller than 90°, increases the efficiency for angles larger than 90°, and hardly affects the diffraction efficiency when this angle is close to 90°. The results for p polarization are obtained, to the best of our knowledge, for the first time. The analysis of angular selectivity of the gratings has shown that the effect of nonlinearity becomes particularly important for light waves incident on the hologram at angles close to the Bragg one. It is also found that, for any thickness of the photosensitive medium, there exists an optimum value of the maximum change in the refractive index, for which the diffraction efficiency may be close to 100% in a wide range of exposures. In this case, the nonlinearity for s polarization stabilizes, to some extent, the dependence of the diffraction efficiency on the exposure.     

Analysis of simultaneous multiple-exposure hologram

The properties of simultaneously recorded multiple hologram are studied. A new model to describe the behaviors of the hologram is proposed. From this model, an analytic formulas of diffraction efficienies are given. It is shown that the efficiencies can not reach at 100％ due to the coupling between diffraction orders through intermodulation gratings. And the comparisions are made for this model with the results by Kogelnik's coupled wave theory for N=1 and those by L. Solymar's model for neglecting the effect of intermodulation gratings respectively. It is shown that these results are in agreement to each other.     

基于光学全息的任意矢量光的生成方法

基于光学全息的角度复用特性, 根据空间光调制器对光场的相位和振幅调制原理, 通过加载产生任意矢量光所需要的相位分布, 设计了一种生成任意矢量光的方法. 该方法首先利用光学全息技术记录空间光调制器加载的相位, 从而制作一个全息光栅; 再现过程中, 两束具有相同入射角度的参考光照射全息光栅, 使得两束再现光相干叠加, 进而获得可调控的任意矢量光. 该方法能够避免复杂偏振态的出现, 并且具有生成光路简单、方便操作、生成矢量光的偏振纯度高等优势. 通过计算机模拟生成了任意矢量光, 获得了很好的效果.     

I/Q intensity-demodulation analog photonic link based on polarization modulator

We experimentally investigate a high-linearity analog photonic link based on polarization-modulation in-phase/quadrature (I/Q) intensity-demodulation. In the proposed system, a light wave with its polarization direction oriented at an angle of 45° with respect to the principal axis of the polarization modulator (PolM) is polarization modulated by a drive signal. In the receiver, the polarization-modulated signal is split into two paths using a 50:50 optical coupler (OC). In each path, a polarization beam splitter (PBS) is connected to the PolM via a polarization controller (PC) to realize the in-phase and quadrature signal, respectively. Thanks to the polarization-modulation to intensity-modulation conversion, the fluctuation of the optical phase noise has no impact on the coherent signals. In addition, the use of a single PolM allows the link avoids the matching requirements of dual modulator schemes. The linearization leads to suppression of the third-order intermodulation (IMD3) by more than 40 dB, compared to the quadrature signal. Experimental results show that the link gain is -11.5 dB, noise figure is 26.5 dB, and the third-order limited spurious free dynamic range (SFDR) is 124 dB in a 1 Hz bandwidth.     

Image reconstruction from a dielectric volume hologram

The phenomenon of image reconstruction from an absorptionless volume hologram is analyzed using coupled-wave diffraction theory. Reconstruction efficiency formulas are derived, which apply when the hologram intermodulation component is negligible and when no extraneous diffracted orders of significant amplitude are generated. Both transmission and reflection holograms are considered, and the analysis is developed for diffraction geometries in which polarization effects are appreciable.     

Orientation of azobenzene molecules in polymer films induced by all-optical poling

A model of the alignment of azobenzene molecules in polymer film induced by all-optical poling is proposed and verified by experiment. We found that when the writing beams of frequencies ω and 2ω are both linearly polarized with their polarization directions parallel to each other, azobenzene molecules tend to reorient to the direction perpendicular to the writing beams polarization. At the end of the writing process, more molecules orient to the direction perpendicular to the writing beams polarization than those which orient to the parallel direction. The alignment of molecules parallel or perpendicular to the polarization of the writing beams is characteristic of polarity or no polarity, respectively. The alignment of molecules along the polarization of writing beams results in the second order nonlinearity in the polymer film. According to the model, a new method to improve the optical poling efficiency is put forward.     

部分相干平顶光束经光阑衍射的偏振特性

根据光束的相干-偏振矩阵和传输理论,对部分相干平顶光束经正多边形光阑衍射的偏振特性进行了系统的研究.给出了部分相干平顶光束偏振度传输公式,并将高斯-谢尔模型光束以及部分相干平顶光束在自由空间传输的偏振度作为特例统一于一般表达式中.研究表明：部分相干平顶光束经光阑衍射的偏振特性与光阑截断参数、光束的空间相干性、衍射角、传输距离、平顶光束的阶数有关. 关键词： 部分相干平顶光束 偏振特性 相干-偏振矩阵 正多边形光阑 光阑衍射     

部分相干平顶光束经光阑衍射的偏振特性

根据光束的相干-偏振矩阵和传输理论，对部分相干平顶光束经正多边形光阑衍射的偏振特性进行了系统的研究.给出了部分相干平顶光束偏振度传输公式，并将高斯-谢尔模型光束以及部分相干平顶光束在自由空间传输的偏振度作为特例统一于一般表达式中.研究表明：部分相干平顶光束经光阑衍射的偏振特性与光阑截断参数、光束的空间相干性、衍射角、传输距离、平顶光束的阶数有关.     

用琼斯矩阵法分析别汉棱镜像面偏振态分布

 基于反射定律的矢量式易于追迹复杂系统中光线的三维空间传播方向,计算了别汉棱镜每一面反射光线的方向,利用琼斯矢量法建立每一反射平面的琼斯矩阵以及面与面之间的传输矩阵,得到了一束线偏振平行光通过别汉棱镜后像面上的偏振状态分布,即经由2个屋脊面出射的光束是2个方位角不同的椭圆偏振光,这2个方位角的大小与入射线偏振光的振动方向有关。采用斯托克斯参量测量法,对别汉棱镜像面上偏振状态的分布进行了实验检测,得到了与理论分析一致的结果,指出别汉棱镜的偏振效应将会导致出射光束偏振状态的不均匀分布。     

反射式光学电压互感器光路建模及偏振误差分析

光路系统的偏振误差极大地制约着准互易反射式光学电压互感器的准确度.借助琼斯矩阵,建立了分立光学器件及光纤熔接点的传输模型,推导出完整的电压互感器光路系统的数学模型.以此模型为基础,对电压互感器中的偏振误差进行了仿真分析.结果表明：光源偏振度、起偏器消光比及起偏器与相位调制器的对轴角度主要影响系统的检测灵敏度|法拉第准直旋光器的旋光角度、法拉第准直旋光器与BGO晶体的对轴角度误差是主要的偏振误差源,影响系统的测量准确度及稳定性|根据电子式电压互感器IEC60044-7 0.2S级标准,法拉第旋光角度误差应该小于1.6°,旋光器与BGO晶体对轴角度误差小于1.85°.该研究对准互易反射式光学电压互感器光路设计和误差抑制具有一定的参考价值和指导意义.     

Rotation of a Fine Particle with Circularly Polarized Anti-Parallel Collinear Laser Beams

We have succeeded in the operation of rotating a fine particle which was held without mechanical contact by circularly polarized laser beams with opposite propagation directions. A polystyrene latex particle 11.9 μm in diameter deformed in a disk-like shape was dispersed in water, and was trapped using the anti-parallel collinear laser beams which were set up so that they had the circular polarization rotating in the same direction. It was observed that the trapped particle rotated in the same direction as the rotation of the circular polarization of light. Inversion of the rotational direction of the circular polarization of light reversed the direction of the rotation of the particle. Although the rotational speed of a particle varied significantly from particle to particle, it was found to be proportional to the laser beam intensity. A typical value for the rotational speed per beam intensity was 2.1 Hz/W.     

转换反射中光自旋霍尔效应的自旋堆积方向

从理论上和实验上研究了转换反射中光自旋霍尔效应的自旋堆积方向的方法,建立了描述光束在空气-棱镜界面反射的自旋堆积模型,揭示了横移与光束入射偏振角的定性关系。研究发现,当入射角小于布儒斯特角时,随着入射偏振角的逐渐增大,自旋堆积的方向发生反转。而当入射角大于布儒斯特角时,自旋堆积的方向不再随入射偏振角的变化而反转。结果表明,在光束入射角为确定值且小于布儒斯特角的情况下,可以通过调控光束的入射偏振角转换自旋堆积的方向。转换自旋堆积方向的研究为有效调控光自旋霍尔效应提供了新的途径。     

Identification of the alignment of azobenzene molecules induced by all-optical poling in polymer film

The alignment of azobenzene molecules in DR19-PUI film induced by all-optical poling is identified. When the writing beams of frequencies ω and 2ω are both linearly polarized with their polarization directions parallel to each other, azobenzene molecules tend to reorient to perpendicular direction (i.e. direction perpendicular to the polarization of writing beams). At the end of the writing process more molecules orient in perpendicular direction than those in parallel direction (i.e. direction parallel to the polarization of writing beams). The alignment of molecules in parallel or perpendicular direction is, respectively, characteristic of noncentrosymmetry or centrosymmetry. It is the alignment of molecules in parallel direction that results in the second-order nonlinearity in the poled film.     

Analysis of Polarization State by Digital Holography with Polarization Modulation

The digital holographic technique is applied to analyze the spatial distribution of polarization state of light transmitted through anisotropic objects using an orthogonal linearly polarized reference beam. The polarization orientation of reference beam is switched by an optical fiber Faraday rotator for successive hologram recording. To confirm the principle of polarization analysis, a quarter wave plate (QWP) is used and the distribution of polarization state over the object surface is analyzed for various orientations of the QWP. By providing an area of a known polarization for a part of the object wave as a reference, a phase drift of the reference waves can be evaluated and compensated for using the reference area. The principal axis and ellipticity of polarization ellipse are calculated and compared with their theoretical values. A good agreement between the experimental and theoretical values is observed.